There are many devices which utilize the injection of a spray of fuel or other liquid during operation. Such devices include, but are not limited to: gas turbine engines, RAM-jets, SCRAM-jets, hydrocarbon dosers and particulate filters.
Gas turbine engines, for example, typically include a compressor section for compressing inlet air, a combustion section for combining the compressed air with fuel and combusting the fuel, and a turbine section where the energy from the hot gas produced by combustion of the fuel is converted into work. The exhaust gas from the turbine section may also be used to achieve thrust or as a source of heat and energy.
Typically, some form of fuel injectors are utilized in the combustion section for spraying a flow of fuel droplets or atomized fuel into the compressed air to facilitate combustion. In some applications, and particularly in gas turbine engines which must run at variable speeds, variable area fuel injectors have been utilized to provide a convenient and inexpensive method to inject fuel into the combustor while also metering the fuel flow to thereby eliminate the need for an additional fuel metering valve.
RAM-jets and SCRAM-jets are similar to gas turbine engines, in that they include a combustor having fuel supplied by a fuel injector, but differ from gas turbine engines in that RAM-jets and SCRAM-jets do not include a turbine section. Hydrocarbon dosers and particulate filters, of the type used to meet emission requirements for diesel engines, for example, sometimes include a combustion chamber, catalytic converter or heat exchange apparatus into or against which a spray of fuel is directed from a fuel injector. In all of these applications, variable flow fuel injectors are sometimes advantageous.
In one previous approach to providing such variable area fuel injectors, a conical-shaped surface at the end of a pintle is spring-biased into a seated position with a corresponding variable flow orifice of an injector housing. The injector housing is mounted in a fuel supply manifold. When pressurized fuel is supplied to the injector housing from the manifold, the fuel pressure overcomes the spring bias and forces the conical-shaped surface of the pintle away from the variable flow orifice in the injector housing, to thereby create a variable area opening between the conical-shaped surface of the pintle and the variable flow orifice. As the pressurized fuel passes through the opening between the conical-shaped surface and the variable flow orifice, the fuel is atomized and directed into a fan-shaped spray. The fuel flow rate, in such a fuel injector, is thus controlled by the combination of factors including the spring characteristics, fuel pressure inside the injector, and the area that is increasingly exposed as the fuel pressure is increased.
Although such variable area fuel injectors work well in many applications, they do suffer from several known drawbacks. For example, due to inherent variations involved with manufacturing and assembling the components of the variable area fuel injector, when operation is required with fuel pressures at or just above the cracking pressure of the nozzle, the flow rates through such valves can be inconsistent. Also, fuel distribution can be poor, due to uneven lifting of the conical-shaped surface of the pintle away from the variable flow orifice. As a result of these and other problems, it is known that the previous approach to proving variable area fuel injectors described above results in injectors which perform well at high fluid flow rates, but at other fuel flow rates which may occur at engine idle, or during cruise operation by an aircraft, for example, where the flow rate can be inconsistent and poor atomization may be experienced.
It is desired, therefore, to provide an improved variable area fuel injector and method of operation of a variable area fuel injector which overcomes one or more of the limitations and problems addressed above. In particular, it is desirable to provide a variable area fuel injector that is capable of delivering consistent and well-atomized flow over a wider range of operating conditions than can be achieved with prior variable area fuel injectors.